Electronic tuning indicator for radio receivers



g- 1952 J. H. VAN WAGENINGEN 2,606,290

ELECTRONIC TUNING INDICATOR FOR RADIO RECEIVERS Filed May 10, 1950 INVENTOR. JOHAN HENDRIK VAN WAGENINGEN AGENT Patented Aug. 5, 1952 ELECTRONIC EUNING INDICATOR FOR RADIO RECEIVERS Johan Hendrik 7 van Wageningen, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn, as

trustee Application May 10,

1950, Serial No. 161,051

In the Netherlands June 17, 1949 Claims. (Cl. 250 -40) This invention relates to electronic tuning devices used in wireless receivers having automatic volume control. In such apparatus it is frequently diflicult to eflect tuning by ear and for this reason use is frequently made of visual tuning. For this purpose an electron-ray indicator may be used, which comprises a discharge tube having a cathode and an anode, and one or more deflection electrodes which are subject to a voltage derived from the detector portion of the apparatus and which impart to the electron beam emitted by the cathode a deflection varying with this voltage. The anode is in most cases conical in shape and is internally coated with fluorescent material, the arrangement being such that the anode may be observed from the upper side of the tube. The tube is arranged in the apparatus in such manner that only the upper side is visible from the outside, the tube being preferably arranged behind an aperture provided in the cabinet of the apparatus. Consequently, when the apparatus is in operation, that side of the anode which can be observed from the outside has produced on it fluorescent spots the dimensions of which are a measure of the accuracy of tuning of the apparatus.

In most cases it is desirable to amplify the control voltage before being supplied to the de-' flection electrodes of an electron-ray indicator. The latter is therefore usually assembled with an amplifying system in a single envelope. This amplifying system may comprise a control grid, an anode connected to the deflection electrodes and a cathode, and the latter may be integral with the cathode of the indicator proper. The control grid has supplied to it a control voltage, whilst the anode is connected by way of a coupling resistance to the positive terminal of the high tension supply. The amplification furthermore affords the advantage that the deflection voltage has the polarity which is generally desired.

It has beenv found, however, that when use is made of such indicators, the optimum variation .of the deflection with signal strength is not always obtained, since in many cases it is desirable that the indicator should not respond to comparatively weak signal voltages and should be- :come operative only when the signal voltage exceeds a certain limit.

In order to obviate this disadvantage, the electron beam is, according to the inventiomnot only amplification of which is controlled as a functio of the signal voltage.

The invention is based on the fact that the width of the fluorescent spot is controlled'by this second voltage only at higher signal strength. The anode of the said amplifying tube is preferably connected through a coupling resistance to the screen grid of a tube controlled inamplification, this screen grid being connected by way of a supply resistance to the positive terminal of the high tension supply. In this case the screen grid of the tube controlled in amplification will have a voltage which increases with increasing signal strength, since the screen grid current decreases with increasing signal strength.

The invention is of particular importance for circuit-arrangements in which an electron-ray indicator having two sensitivities is provided. These two sensitivities are usually obtained by utilising two amplifying systems, the control grids of which are interconnected, but of which one control grid, for example due to its being wound with a different pitch, imparts to the associated amplifying tube an amplification factor which is different from that of the other amplifier. The indicator portion comprises two deflection systems, of, which one is subject to' the action of the voltage at the anode of one amplifier and the other to the action of the voltage at the anode of the other amplifier. As a rule, two luminous spots are then visible on the fluorescent screen of the indicator whilst the deflection systemsact upon the width of the shade sectors between these spots. Since the two amplifiers have different amplification factors, the angular variation of one sector upon variation in signal strength and tuning is much quicker than that of the other, i. e. the sensitivity of one sector is much greater than that of the other sector. Onesector may serve for tuning to stations the signal strength of which is comparatively small and the other sector for tuning to stations having a greater signal strength.

The disadvantage of such a device is that, when the grids of the amplifiers are'connected. toa resistance included in the detector portion of the receiver, the less sensitive portion operates upon reception of comparatively weak signals and may already exhibit a comparatively great de-"" "flection. I It is thus frequently impossible to tune to local transmitters by the visual indicator. By applying the invention to the indicator portion" having the smaller sensitivity, this portion will not respond to the reception of stations the signalstrength of which lies below a certain limit, so

that the opening angle of the shade sector of the insensitive portion does not increase until the signal strength of the received station has a comparatively high value.

In order that the invention may be readily carried into'effect, one example of the invention applied to such a device will now be described in detail by reference to the accompanying drawing which is a schematic circuit diagram showing that part of the arrangement which is essential to the invention.

In the figure, reference numeral I designates the input terminals of an input band-pass filter comprising two circuits 2 and 3 and to which the incoming intermediate frequency oscillations are supplied. Tube 4 is an intermediate frequency amplifying tube having a cathode 5. and a control grid 6 which has supplied to it the intermediate-frequency oscillations. thermore comprises a screen grid 1, which is connected by way of .a resistance 33 to the positive terminal of a source of supply, and a suppressor grid 8, connected to the cathode. The first circuit 9 of a second intermediate frequency filter 9, III! is connected to the anode. A tapping on the coil of the second circuit In is connected to the anode of a detector tube II, the cathode of which is grounded. The detector circuit furthermore comprises two series-connected resistances I2, l3, the second of which has derived from it the low-frequency modulation voltage which is supplied to. terminals Id. The condenser I operates as :a short-circuit for the. intermediateirequency currents.

Furthermore, provision is made of automatic volume, control. A voltage of intermediate frequency isv derived by way of a condenser H from the circuit 9 and supplied to a diode anode l5- incorporated in the tube 4- diode circuit furthermore comprises a resistance l8, across.

which occurs not, only the modulation frequency but. also direct voltage which is proportional, to the amplitude of the carrier wave. and which serves as a. control voltage. for the automatic volume control. This voltage issupplied by way of a filter comprising a resistance l9 and a condenser 23. to the grids of thepreceding high-ire quency and. mtermediate-frequency amplii ying' tubes. The, amplification of the intermediatefrequency amplifying tube 4 is controlled by the direct voltage which is taken from the resistance l3 and which is likewise. proportional with theamplitude. of, the carrier-wave. This direct voltage isvsupplied to the. lower end of circuit ,3 by y of. a filter comprising a resistance 2| and a condenser 22.

For the indication ofv tuning, provision ismade of a tube 23 having a cathode common to a plurality of electrodesystems andconnected-to-earth.

The tube comprises two triode amplifiers, the

grids 2.5. of which are interconnected, whilst an anode, 28 is connected by wayof a coupling resistance 3| to the positive terminal of the source of, supply voltage. The grid associated with this anode is. wound with a. pitch smaller than that of, the grid associated with. asecond. anode. 21- so that. thega-in .factor of the first, triodeis. greater than that of 'the'second triode. Tube. 23- furtherinore'comprises. an indicatorfsystemhaving ananode 3.0 and two deflection electrodes 28 andv 2-9' which, as. a rule. have theform of rods, The

anode is covered inlmownmanner with fiuores cent material and the defiectionelectrodes are-so positionedthat. two luminous spots separated by shade sectors are. seen onthe cathode. The de-- The tube fur- 4 flection electrodes 28 and 29 are connected to the anodes 2B and 21. The voltage set up across resistance I3 is active at the grid 2 5.

The operation of the arrangement described is such that if the voltage across resistance I3 increases, for example due to an increase in signal strength as a result of the correct point of tuning being approached, the electron current flowing to the anode 26 decreases so that the voltage at the anode itself increases as a result of the voltage loss across the resistance 3! and one shade sector on the. fluorescent screen of the anode decreases in width. With correct tuning the width of the shade sector is as small as possible. The voltage across resistance I3 is also active at the grid of the second triode the sensitivity of which, however, is much smaller so that the voltage at the second deflection plate 28, upon variation in the voltage across resistance I3, is varied to a much smaller extent and the associated shade sector shows a much smaller decrease in width.

It. has been common practice to connect the anode, 21, similarly as the anode 26, by way of a coupling resistance to a point of constant potential. However, in this case undesired variation in the width of the shade sector still occurs upon reception-of weak stations. According to the invention, this disadvantage is. obviated by connecting the anode 21 by way of a coupling resistance 32 to the screengrid' T of the tube 4., controlled in amplification. It is thus achieved thatthe-voltage atv the anode 21 for a small'.sig nal strength has so small a value that variation inthe shade sector corresponding to the defiec-; tion plate '28 substantially doesnot occur up to. a predetermined limit. of the signalstrength. It is only upon receptionv of strong signals that. the control voltage at the controlgridfi' of the tube 4- has, so high anabsolute value that a high voltage is set up at the screen grid so that a controlling, actionisexerted' upon the shade sector associated with deflection plate 28. Furthermore, the triode 24; 25; 21 may also exert a controlling action-Lin the normalway, although this not alwaysrequiredfor satisfactory operation of the device.

gridlead, there willbe an increase in the voltage at the screen grid from to substantially 250- volts, if the signal voltage varies from -a given minimum value into a high maximum value.

Consequently, in the circuit-arrangement according tothe invention, the width of the shade sector for the indication at great signal strength. is controlled not only by the variation. in: the anode. current of the. amplifying triode, whichds:

due to variation in-the voltage at the control grid, butalso by the variation in the voltage: at; the anodexas a result of the variation'insupply voltage, the last-mentioned control as a rule being the main control. readily possible to providean adjustment at w'hich the insensitive portion of thexindicator. circuit;

does not become; operative until: the extreme working limit of the sensitiveportionisattained; The operation may even. be slightly improved by including. a resistance. 35. between the anode of the insensitive triode and earth. Thisireisistance may have a' value of about 2 'megohms; Thecircuit-arrangement according. to the.- in

vention thus-affords the advantage oft'a' material It has been found: that. it is:

improvement in operation without additional elements being required.

What I claim is:

1. In a radio receiver provided with an intermediate frequency amplifier including an electron discharge tube having a screen grid electrode and an electrode, a detector coupled to the output of the intermediate frequency amplifier and means to automatically control the volume of said intermediate frequency amplifier in accordance with the detected signal, a tuning indicator for said receiver comprising an electron ray tube having an amplifier section and a cathode-ray indicating section provided with a deflection system and a fluorescent target, means to supply the detected signal to the amplifying section of said electron ray tube, means to derive a control signal from one of the electrodes of the tube in the intermediate frequency amplifier, and means to supply said control signal to said electron ray tube whereby the resultant visual indication of said target is dependent both on said detected signal and said control signal.

2. A radio receiver asset forth in claim 1 wherein the control signal is derived from the screen grid electrode of the tube in the intermediate frequency amplifier.

3. In a radio receiver provided with an intermediate frequency amplifier including an electron discharge tube having a screen grid electrode and an anode electrode, a detector coupled to the output of the intermediate frequency amplifier and means to automatically control the volume of said intermediate frequency amplifier in accordance with the detected signal, a tuning indicator for said receiver comprising an electron ray tube having an amplifier section and a cathode-ray indicating section provided with two deflection elements, an electron beam source and a fluorescent target, means to supply the detected signal through the amplifying section of said electron ray tube to one of said deflection elements to effect beam deflection with respect to-said target for detected signals of low signal strength, means to derive a control signal from one of the electrodes of the tube in the intermediate frequency amplifier, and means to supply said control signal to the other of said deflection elements to effect beam deflection with respect to said target for detected signals of increased signal strength whereby the resultant visual indication of said target is dependent both on said detected signal and said control signal.

4. In a radio receiver provided with an intermediate frequency amplifier including an electron discharge tube having a screen grid electrode and an anode electrode, a detector coupled to the output of the intermediate frequency amplifier and means to automatically control the volume of said intermediate frequency amplifier in accordance with the detected signal, a tuning indicator for said receiver comprising an electron ray tube having first and second amplifier sections, the amplification factor of said first amplifier section exceeding that of said second amplifier section, and a cathoderay indicating section provided with two deflection elements and a fluorescent target, means to supply the detected signal through said first amplifying section of said electron ray tube to one of said deflection elements, means to derive a control signal from the screen grid electrode of the tube in the intermediate frequency amplifier, and means to supply said control signal through said second amplifying section of said electron ray tube to the other of said deflection elements whereby the resultant visual indication of said target is dependent both on said detected signal and said control signal.

5. A radio receiver as set forth in claim 4 wherein said second amplifier section is provided with an output electrode which is resistively coupled both to the screen grid electrode of the tube in the intermediate frequency amplifier and to a point of constant potential.

J OI-IAN HENDRIK VAN l/VAGENINGEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,190,435 Roberts Feb. 13, 1940 2,451,584 Stone Oct. 19, 1948 2,457,016 Vilkomerson Dec. 21, 1948 

